The present invention relates to tank vehicles such as railway tank cars and, in particular, to arrangements for heating the lading contained therein.
In order to provide heat necessary for the unloading of certain commodities shipped in railway tank cars, the tank cars are traditionally equipped with heater coils through which steam is introduced at an unloading rack until the proper commodity temperature for unloading is reached. Such an arrangement is disclosed in U.S. Pat. No. 3,685,458, issued Aug. 22, 1972, and assigned to the assignee of the present invention. That arrangement requires extensive steam facilities at the unloading terminal, and also requires considerable labor and time in connecting and disconnecting each car with respect to a steam line.
Another type of heating arrangement is disclosed in U.S. Pat. No. 3,286,079, issued Nov. 15, 1966, and includes elongated tubes extending longitudinally within the tank and in which are received long electrical resistance-type heating units. But this arrangement occupies valuable lading space within the tank, is of costly construction, and utilizes large amounts of electric power for energizing the long heating units which extend substantially the entire length of the tank. The long electrical heating units must be provided with special shock-absorbing mountings to prevent damage to the heating units from the sudden and often severe jolts and impacts commonly undergone by railway cars in use. While the arrangement is susceptible of energization from an onboard power source, an internal combustion engine is necessary for this purpose because of the large amounts of power which must be provided.
Another type of heating system powered by an onboard power source is disclosed in the U.S. Pat. No. 3,372,693, issued Mar. 12, 1968, and assigned to the assignee of the present invention. That system utilizes an onboard flameless combustion heater, the flue gases from which are passed through heating conduits on one end of the tank. But that system and all arrangements which utilize onboard combustion means suffer from serious practical drawbacks in terms of reliability and safety. More specifically, such systems are subject to mechanical failures in transit and typically require heavy maintenance. Furthermore, they require the provision of an onboard fuel supply, with the attendant risks of fuel leaks and accidental fire or explosion in the jarring environment of a railway car.